PC 34

TRANSITION FROM DISPERSIVE TO NON-DISPERSIVE TRANSPORT IN CONJUGATED POLYMER DEVICES

L.F. Santos^a,b, G.C. Faria^b,c, R.M. Faria^b, A.R. Andrade^c, S. Mergulhão^c

^aDepartamento de Física, Instituto de Biociências, Letras e Ciências Exatas, Universidade Estadual Paulista, Rua Cristóvão Colombo, 2265, 15054-000, São José do Rio Preto, SP, Brazil

^bInstituto de Física de São Carlos, Universidade de São Paulo, C.P. 369, 13560-970, São Carlos, SP, Brazil.

^cDepartamento de Física, Universidade Federal de São Carlos, CP 676, 13565-905, São Carlos, SP, Brazil.

In this work, time-of-flight technique has been used to study the transport behavior of both type charge-carriers (electrons and holes) in thin films of poly(2-methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) deposited onto n-type Gallium Arsenide (n-GaAs) and indium-tin oxide (ITO) covered glass substrates, with semitransparent metallic electrodes on top. The technique is based on the measurement of current transients due to the drift by an external electric field of photogenerated charge-carriers produced by a short (in the order of ns) nitrogen laser pulse. Since the optical density of the films is usually high for the excitation wavelength, the photogeneration of electron-hole pairs occurs mainly near the incident surface and the transient photocurrent through the polymer bulk is practically dominated by single-type carriers (depending on the polarity of the applied bias). Different metallic top electrodes and substrates were used in order to determine the energy barriers at the polymer/electrode interfaces. The transit time and the carrier mobility dependence on the electric field and temperature have been examined in the framework of dispersive transport model, characterized by the energetic and spatial disorder inherent to polymeric systems.